Autodeposition, also referred to as chemiphoresis, autophoresis, and/or autophoretic deposition, is an aqueous immersion process for coating metal that is driven by reactions between the coating and the metal substrate surface when small amounts of multivalent metal ions are slightly solubilized and released from the metal surface leading to destabilization and deposition of the composition at the surface. The aqueous composition for coating the metal can contain a polymer dispersion. For example, one feature of an autodepositable coating can be that the dispersed material is stabilized by functional groups on the polymer and/or provided by surface active agents which are sensitive to multivalent ions entering the aqueous phase. Deposition can occur by interaction between the multivalent ions and the functional groups, causing the dispersion to precipitate on the surface when sufficient concentration of multivalent ions occurs at the metal surface. The multivalent ions can also crosslink the dispersion particles via reaction with particle surface carboxyl groups and/or with other functional surface groups and with the metal substrate.
Examples of autodepositing compositions are disclosed, for example, in European Patent Publication 0132828, Bashir M. Ahmed, U.S. Pat. No. 4,647,480, and Wilbur S. Hall, U.S. Pat. Nos. 5,691,048, and 4,657,788, and patents cited therein. Such compositions can be designed to be particularly effective when a resin material is provided in the form of a dispersed polymer such as a sulfonate-functionalized novolak, or latex made from the emulsion polymerized product of, for example, at least two polymerizable ethylenically unsaturated monomers.